Black polyurethane slabstock foams [e.g., foam colors when substantially all of the light in the visible electromagnetic spectrum (400–700 nanometer) is absorbed] are utilized in a variety of articles, including, without limitation, high fidelity speakers, earphones, and the like. Such black colorations are generally provided through pigments or pigment mixtures or through polymeric colorant mixtures (of various colors, such as mixtures of blue, yellow, red colorants). Black colorant compositions may be individual pigments or mixtures with other pigments (particularly other black pigments) or mixtures of two, three or more individual polymeric colorants. Such mixtures generally complement each other to absorb light across the visible spectrum. For example, orange and blue; yellow, red and blue; and orange, blue and purple represent color combinations which will create a black composition. In general, a black colorant composition of one or more black pigments or combinations of two or more dyes or polymeric colorants will absorb electromagnetic radiation across the entire visible spectrum, but the absorbance at each wavelength may not be uniform. Consequently, the absorbance of such a composition may be represented by a series of peaks and valleys across the visible spectrum such that any loss or modification of any of the component absorbance levels may result in the change of jetness or even the hue of the target black coloration.
Polymeric colorants have become the preferred coloration method in industry for colored polyurethane products, such as foams, resins, and the like. Being liquid in nature, these polymeric colorants contain hydroxyl terminated polyoxyalkylene chain (or chains) and actually tend to react to and within the urethane during polymerization. As a result, the color is integrated within the foam and provides excellent uniformity and depth throughout the entire article. Generally, these colorations are performed in situ during foam, resin, etc., formation. For instance, polymeric colorants (i.e., polyoxyalkylenated colorants), such as those described in U.S. Pat. No. 4,284,279 to Cross et al., have been introduced within polyol compositions during slabstock foam production. The “colored” polyol then reacts with an isocyanate composition to form the desired colored foam. Such foamed products require the presence of a catalyst or catalysts to effectuate the desired reaction between the polyol and isocyanate components.
Potential jetness shifts may be caused by improper mixing of component colorants, uneven lighting for viewing, light exposure (and thus, for example, UV degradation of components), and the like. In essence, deep, dark, jet-black shades are generally difficult to provide within such polyurethane foam articles due to the potential for the individual shades (yellow and/or red) either to absorb insufficiently or in excess at maximum wavelengths to the extent that imbalanced absorption by the individual coloring components therein may, in effect, impart a limited jetness appearance (through increased yellowness, redness, or both).
As for black pigments, the colorations are mostly provided by single sources (unless mixtures of different black pigments are present). However, such coloring agents appear to exhibit a limit to color depth, most likely due to the absorption levels inherently provided by the individual pigments themselves. A broad absorption peak, such as that typically exhibited by such pigment materials, imparts a limited jetness effect within certain target articles, most notably here, for black polyurethane slabstock foams. The limited jet-black appearance is most likely the result of certain wavelengths within the absorption spectrum of the specific pigment particles either being “masked” or impeded from view or being too prevalent for perception by the naked eye. The result is a perceived color that is, generally, too yellow or red to impart a deep, dark color within the target black foam. As a result, the resultant yellowing or reddening of the black color compromises the desired jetness thereof, thereby rendering a black coloration exhibiting a limited jetness appearance (empirically).
Therefore, as discussed and/or alluded to above, such black colorations (provided by either pigments or polymeric colorants) typically suffer from a lack of strength, particularly in terms of presence of limited amounts of coloring agents therein, to the extent that the depth of black colorations within the target foam is aesthetically lacking due to such limited jetness appearance. Improvements have been attempted, most notably through increases in the amount of pigment (carbon black, for example) or polymeric black colorant (REACTINT® X77, from Milliken & Company, for example) added; however, in such a manner, the cost of production increases while the relative improvement in color strength is not proportionally better. Such a disparate result thus has led to a return to certain lower levels of pigment or polymeric colorant utilized with the same aesthetically displeasing low-color-strength black results prevalent.
Also, due to the limitation of the existing state of the art dispersion technology, the amount of pigment (carbon black, for example) can be dispersed into liquid media is limited due to extremely high viscosity. Current commercial carbon black dispersions are thus limited in color strength (e.g., the L* value) even with maximum loadings of pigment dispersions or a mixture of polymeric colorants within target foams without affecting ultimate polyurethane foam performance primarily due to high unwanted yellowness and, possibly, redness, levels measured within those previously made black polyurethane foams.
Improvements within the aforementioned polymeric colorant mixtures are as difficult to provide, primarily since the determination of proper levels of each component color can be altered when greater amounts of the total black colorant are introduced within target slabstock foams. Thus, modifications in flairing appearance, or, at least, in the redness and/or yellowness, thereof, are quite possible, such that the desired high-color-strength black foam is difficult to achieve. A simplified procedure and/or formulation to provide such desired high color strength results is thus necessary; unfortunately, to date, such a formulation has not been provided the black polyurethane slabstock foam industry.